A protractor is a tool used to measure as well as draw angles. This tool is usually semicircular, but a full-circle 360-degree version is also available. If looking at this tool really leaves you confused, never fear; Learning to use this tool is relatively easy. By understanding how parts of a protractor work together and following these few easy steps, you'll be an angle expert in no time.
Method 1 of 2: Measuring Angles with a Protractor
Step 1. Estimate the size of the angle you have
Angles can be classified into three groups: acute, obtuse, and right angles. An acute angle is narrow (less than 90 degrees), an obtuse angle is wide (greater than 90 degrees), and a right angle is 90 degrees (the two lines that form it are perpendicular). You can identify the category of angle you want to measure just by looking at it. Determining the angle category in the first step helps you identify which scale on the protractor to use.
At first glance, we can tell that the angle is acute because its size is less than 90 degrees
Step 2. Position the base or vertex of the angle you want to measure at the center point (center of the arc)
The small hole in the middle of the protractor's baseline is the base. Make the vertex of the corner coincide with the center of the cross at the base.
Step 3. Rotate the protractor to make one of the legs of the angle coincide with the base line of the protractor
Position the vertex of the angle at the base of the protractor, then slowly rotate the protractor so that the foot of the angle falls above the base line of the protractor.
The base line of the protractor is parallel to the edge of the protractor, but the baseline is not the edge of the protractor that is even. The base line coincides with the center of the base (center of the arc) and the line extends to the starting point of the scale on both sides (left and right)
Step 4. Follow the legs of the opposite corners (lines) up the scale of the protractor
If the line does not cross the arc of the protractor, extend it so that it passes through it. Alternatively, you can place the edge of a sheet of paper close to the foot of the corner (line) and then extend the line until it passes through the arc of the protractor. The number crossed by the line is the measure of the angle in degrees.
- In the example above, the measure of the angle is 71 degrees. We know to use a smaller scale because in the first step we determined that the angle measure is less than 90 degrees. If the angle is obtuse, we will use a scale that marks an angle greater than 90 degrees.
- At first, the measurement scale may seem confusing. Most protractors have two opposing rulers, one on the inside and the other on the outside. Such a design makes this tool easy to use for measuring angles from any direction.
Method 2 of 2: Drawing Angles with a Protractor
Step 1. Draw a straight line
This line will be the reference line as well as the first leg of the angle you want to draw. This line will be used to determine the position where you should draw the second leg of the corner. Usually the easiest is to draw a straight line in a horizontal position on the paper.
- To draw these lines, you can use the even edges of the protractor.
- Line length is not specified.
Step 2. Position the base of the protractor at one end of the line
This point will be the vertex of the angle you are going to draw. Mark on the paper, exactly where the peak is placed.
You don't have to put the dot at the end of the line. The point can be placed anywhere along the line, but it's easier to just use the end of the line
Step 3. Find the degree value for the angle you want to draw on the proper protractor scale
Make the reference line coincide with the base line of the protractor, then mark the paper at the size of the degree you want. If you are drawing an acute angle (less than 90 degrees), use a smaller number scale. For obtuse angles (greater than 90 degrees), use a scale with a larger number.
- Remember that the baseline is parallel to the edge of the protractor, but the baseline is not the edge of the flat protractor. The base line coincides with the center of the base (center of the arc) and the line extends to the starting point of the scale on both sides (left and right).
- In the example above, the angle measure is 36 degrees.
Step 4. Draw a second leg to complete the corner
To draw the second leg, connect the vertices to the marked degree measure. Use a ruler, the flat edge of the protractor or the straight edge of another tool. The second leg will complete the angle you made. To check the accuracy of the angle you have drawn, use a protractor to measure it.